Components of certain equipment, such as that used in the petroleum and petrochemical industry, which includes the exploration, production, refining, manufacture, supply, transport, formulation or blending of petroleum, petrochemicals, or the direct compounds thereof, are often monitored to maintain reliable operation. However, such components can involve harsh conditions, such as high temperature, high pressure, and/or a corrosive environment, making it difficult or costly to obtain reliable measurements.
Deposits, such as debris, bio-growth, inorganic or organic fouling, coking, or the like, on the surface of a component in connection with petroleum and petrochemical operations, such as those in refineries, chemical plants, and oil and gas processing plants, are generally undesirable. For example, deposits on components such wash beds, trays, or packing of distillation towers, reactors, heat exchangers, furnace tubes, or the like can cause unplanned capacity loss, excessive cost of equipment maintenance, and increased energy usage.
Undesirable deposits can result from a number of causes in a refinery or the like. For example, the processing of a hydrocarbon-containing feed streams at elevated temperatures in a processing zone, such as a furnace, heat exchanger, distillation tower or other refinery equipment, can result in the formation of carbonaceous substances which can deposit on surfaces of the equipment. Such carbonaceous substances are generally referred to as “coke” in the fields of petroleum refining and petro-chemical processes. Coke deposition on equipment surfaces can alter the operation of the equipment, usually in an undesirable manner. For example, feed streams are heated in a furnace before being introduced to distillation columns. Formation of coke can result in a blockage of tubes in the furnace, as well as the blockage in the transfer lines from the furnace to the distillation column. The coking on tube surfaces can also decrease the heat transfer, and therefore reduce the energy efficiency of the furnace. Additionally, coking often occurs in the column itself, typically within wash beds or at interfaces between different types of packing or the like. Coking can also occur in the bottom of the tower and plug liquid outlets and pump strainers, causing pump cavitation and damage.
Measurement of the distribution of deposits, such as coke, can provide for enhanced operation strategies. For example, detection of the onset of coking in a wash bed of a vacuum pipe still distillation tower can allow mitigation techniques (such as application of a high flow rate of wash oil) to be appropriately applied.
Conventional techniques for detection of such deposits can include point measurements (e.g., using ultrasonic thickness measurements), pressure drop measurements, and bulk heat transfer estimation techniques. For example, detection of coking in refinery equipment, including distillation towers, distillation tower bottom circuits, distillation tower feed furnaces, and coker feed furnaces and transfer lines, has been addressed with measurement of pressure drop. However, this technique is not without disadvantages, such as for vacuum tower wash beds, where the pressure drop is typically only on the order of a few mmHg in these wash beds when coking occurs. Additionally, pressure measurements cannot tell where (either the axial location or the diametric location) the deposits are occurring in the wash bed. Thus, pressure measurement can be a highly unreliable indicator of coking. Similarly, temperature differentials between bulk temperatures have also been used to detect coking. However, this technique involves a gross measurement and thus not necessarily accurate.
Accordingly, there is a continued need for improved techniques for detecting deposits in a vessel.